Patent literature 1 describes a switch device according to the prior art. The switch device according to patent literature 1 includes several switch portions formed by a detection electrode. Each switch portion includes a light source corresponding to each detection electrode. The detection electrode and the light source are connected to a switch circuit. The switch circuit includes a selection switch to select a first connection state or a second connection state. The first connection state connects all detection electrodes to one dedicated detection circuit. The second connection state connects each detection electrode to a discrete detection circuit.
The light source turns off when a user's finger does not approach the switch portion. The selection switch allows all the detection electrodes to maintain the first connection state. All the detection electrodes are connected to the dedicated detection circuit to increase an apparent area for the detection electrodes and provide high sensitivity.
When the user's finger approaches the switch portions, the dedicated detection circuit outputs a first detection value (capacitance change). When the first detection value exceeds a predetermined first threshold value, all the light sources turn on. The selection switch changes the detection electrodes to the second connection state. The detection electrode corresponds to the discrete detection circuit on a one-to-one basis. Each detection electrode provides the standard sensitivity.
When the user's finger approaches one of the switch portions, the discrete detection circuit connected to the detection electrode for that specific switch portion outputs a second detection value. When the second detection value exceeds a predetermined second threshold value, only the light source corresponding to the specific switch portion turns on. The light sources corresponding to the remaining switch portions turn off.
According to patent literature 1, each light source is controlled to turn on or off depending on the state of an operator's finger approaching each switch portion. This aims at improving operability in a dark place. The selection switch provides the first connection state to enable the detection by improving the apparent sensitivity of each detection electrode. The selection switch provides the second connection state to enable the detection at respective detection electrodes based on the standard sensitivity. The state of approaching user's finger can be detected with stable accuracy.